Lots of replies far to one side or the other ITT, with few people really thinking critically.
First, can we clarify that if you run sub-16, you will earn $100k for that year, and that year only? Because if you only had to run sub-16 once, and be guaranteed $100k/year for the rest of your life, the incentive is MUCH greater.
As it stands, $100k for just one year isn't actually that great of an incentive for someone to "train their whole life" to achieve. Which is, more or less, what a relatively large percentage of people would have to do to achieve sub-16.
Before estimating the # of people that would actually find this to be a worthwhile pursuit, it might be helpful to think about the actual maximum percentage of men who could realistically run sub-16 assuming INFINITE incentive.
That's to say, if every male human born were trained from birth with the sole goal of running sub-16 at some point in their life, how many could actually do it? Let's assume that we live in a society where you will be executed at age 30 if you have failed to run a single sub-16 by that age.
Within one generation or so, I think we'd be at 50%. And if you go farther out into the future, in a purely running-based society like this, it seems as though we would self-select that number ever higher, until it's virtually 100%.
Remember, we're talking about children being guided from birth toward a running lifestyle, receiving optimal training throughout their youth, and given the time and incentive required to do their best. A completely different society than the one in which we reside.
Back to the original hypothetical. The number is going to be lower than 50%. By far. Because when you think about the idea that you'll need to stay in sub-16 shape to actually make a "career" out of this, the incentive drops for many people.
The lengths some folks would have to go to to reach sub-16 would probably prevent them from having a normal career. And even 5-7 years at $100k per year isn't that great. What are you going to do when you're done? You'll be ages behind your peers who went right into the regular workforce.
I don't know what percentage of men can currently run sub-16, but let's just say it's 0.1%. I doubt we'd see a jump to anything higher than 1.0% given the $100k/year scenario proposed in the OP. It's just not that valuable unless you can EASILY crack sub-16 and continue to do so for years. It's not worth it to put in 10 years of 90-mile weeks for a single $100k payday.